Sandra Barnett, 49, wife of former NFL player Buster Barnett, was shot and killed Wednesday by a woman friends say was her husband’s mistress, before the woman turned the gun on herself WSB-TV reports.

Barnett, who worked as a special needs teacher at McNair Middle School in Dekalb, Ga., was talking on the phone at her home when Lisa Brown allegedly knocked on the door.

“She said, ‘Open this door before I kill you. Open this door or you’re going to die,’” said Ruby Chester, who was on the phone with Barnett.

Chester called 911, then she and friends, including Barnett’s brother, John Brooks, went to her home to check on her.

When they got there she was gone.

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Police believe Lisa Brown, a former teacher for Atlanta Public Schools, forced Barnett to leave with her in a black Dodge Durango owned by Barnett’s husband.

A friend saw the SUV Brown was driving leave the subdivision, not realizing Barnett was inside.

Investigators put out an alert for the SUV.

Police tracked Brown’s cellphone into Alabama and Mississippi.

Wednesday afternoon, deputies with the Carroll County Sheriff’s Office spotted the vehicle and chased it into Alabama. Officers said the SUV stopped on Interstate 20 and they saw Brown pull a handgun, shoot Barnett and then shoot and kill herself.

Chester said she had warned her friend about the woman who had been having a relationship with Barnett’s husband.

“A couple times, she would see her car parked out in front of her door,” Chester said. “I’m just sad, because it didn’t have to happen, and I told her to do something about that woman being so aggressive toward her.”

Brown taught at North Atlanta High School and was with the system from 2008 until 2013, reports 11Alive.com.